Drip irrigation systems have come into widespread use in the agricultural area. Drip irrigation systems supply water at a slow, controlled rate to the root zone of the particular plants being irrigated. Typically, drip irrigation is accomplished by providing a low volume water outlet at each plant that permits a limited dripping of water directly to the root zone of the particular plant. Because evaporation, runoff, overwatering, and watering beyond the root zone are eliminated, substantial water and nutrient savings are realized. In addition, drip irrigation reduces contaminants to the water table by enabling the farmer to supply only enough water and fertilizer to reach the plants, reducing excess water that would run off and contaminate the water table below.
Drip irrigation hoses tend to be relatively long to be able to extend across a field. As the water travels along the hose away from the water source, the pressure of the water decreases. Thus, the water pressure at the beginning of the hose (near the water source) is greater than that at the far end of the hose. Because the drip rate of the hose is a function of the water pressure, the drip rate at the beginning of the hose tends to be greater than at the end of the hose. Other field conditions, such as elevation, also affect the pressure, and thus the drip rate, along the length of the hose. However, it is often desirable to have a relatively uniform drip rate along the length of the hose. Moreover, other varying field conditions, such as soil type and drainage, create a need to have different drip rates throughout the field to compensate for the different field conditions.
One proposed solution to the pressure variation problems is to incorporate pressure-compensating emitters into the hoses to reduce the effect of the pressure difference over the length of the hose on the drip rate along the length of the hose. Such hoses are described in U.S. patent application No. 09/308,060, entitled "Pressure-Compensating Drip Irrigation Hose and Method for Its Manufacture". However, although these designs address certain pressure-compensation issues, they do not provide a way to provide predetermined drip rates that vary along the hose.